Archive:   VOLUME:   No:   

Volume: 1996/2

Title: Accelerated Aging of Low-Density Cement-Bonded Wood Composites Made Conventionally and With Carbon Dioxide Injection
Author: Robert L. Geimer, Mario Rabelo de Souza, Ali A. Moslemi

The purpose of this study was to evaluate the durability of low-density cementbonded wood composites using an accelerated aging process. Low-density cement-bonded wood composites were made with two types of wood particles (excelsior and splinter) and pressed either conventionally or with carbon dioxide injection. In the conventional boards, calcium chloride and sodium silicate were tested as additives to improve wood to cement bonding. Calcium hydroxide and a mixture of calcium hydroxide and sodium silicate were added to portions of the CO2-injected boards. All the boards were tested before and after 10 cycles of a 3-day soak/freeze/thaw/dry cycle. Boards injected with carbon dioxide showed better initial physical and mechanical properties and also better performance after accelerated aging than did conventionally pressed boards. Excelsior board outperformed splinter board in all conditions tested. No difference could be attributed to additives in either the conventional or the CO2-injected boards. In all treatments, flexural modulus of elasticity retention was less than 50% after 10 czcles of aging, and modulus of rupture was less than 75%. The analysis indicated that freezing had no effect on aging.

Title: Processing of Bog-oak (Ouercus robur, Erch) into Fine Veneer
Author: Franjo Penzar, Hrvoje Matušić

Wood which has been exposed for a long time to running or stagnant water undergoes changes in colour as well as in some physical and mechanical properties. Subfossil wood or abonos is dark brown to black. The change in colour is a result of the decomposition of the wood components. This is not due to the action of micro-organisms but is a consequence of the joint action of a number of factors in water and of the reaction of salts of iron in water with the tannins in oakwood. The length of oakwood exposure to water has been estimated according to the intensity of the discoloration, iron salts content and by the C-14 carbon test. Bog-oak and recent oakwood were cut into precious veneers 0.6 mm thick which are used for the production of costly fumiture, interior design, musical instruments, marquetry, decorative boxes etc.

Title: Improving the Glued Joint Strength by Modifying the Beechwood (Fagus sylvatica L) with Gamma Rays
Author: Andrija Bogner, Boris Ljuljka, Ivica Grbac

The reserach was done on the effects of gama rays on the change of the critical surface energy γc, work of adhesion Wa, penetration Wp, spreading Ws, and the change of the glued joint strength in beechwood. The samples absorbed the irradiated dosages of 25,50 and 100 kGy, which was followed by measurements of the wetting angle. The surface parameters were calculated from the wetting angle and the surface tension of the liquid. The results show the increase of all observed parameters with an increased dose of radiation. The glued joint strength did not significantly change at low absorbed irradiated dosages of 25 and 50 kGy, but at 100 kGy, the increase in shear strength of the glued joint was considerable.

Title: Computer supported kiln devices
Author: Stjepan Pervan, Ivica Grbac

This paper surveys the characteristics of drying kiln control devices presently used in practice. These control devices are specially developed for this purpose, in attempt to achieve the automatic, economic and precise control of the drying process, without the necessity for constant supervision by the highly qualified technical stuff. During the development of these control devices, previous experience was used which was based on scientific and practical knowledge about wood drying field and additionally supported by latest development / applicattion of the computer technology.

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